In general, a level shifter serves as an interface between circuits using different power supply voltages. For example, a signal for driving a word line driver swings between an external voltage VDD and a ground voltage VSS, whereas a signal used in a word line driver swings between a high voltage VPP and a ground voltage VSS. Thus, if two circuits are connected without level shifting, a leakage current may flow in a circuit using a high voltage VPP as a power supply voltage. Therefore, a level shifter is used to connect two circuits.
With increased integration density of semiconductor memory devices, a signal swinging between an external voltage VDD and a back-bias voltage VBB is required to reduce leakage current. Thus, a signal swinging between an external voltage VDD and a back-bias voltage VBB is generated by using a level shifter to level-shift a signal swinging between an external voltage VDD and a ground voltage VSS.
However, in a semiconductor memory device, a signal swinging between a peri voltage VPERI and a ground voltage VSS may need to be level-shifted to a signal swinging between a power supply voltage VDD and a back-bias voltage VBB. In this case, the semiconductor memory device may have two level shifters: a level shifter for level-shifting the signal swinging between the peri voltage VPERI and the ground voltage VSS to generate a signal swinging between the power supply voltage VDD and the ground voltage VSS, and a level shifter for level-shifting the signal swinging between the power supply voltage VDD and the ground voltage VSS to generate the signal swinging between the power supply voltage VDD and the back-bias voltage VBB.